Release of imnumoreactive luteinising hormone-releasing hormone and thyrotrophin-releasing hormone from hypothalamic synaptosomes

Abstract

THE hypophysiotropic hypothalamus regulates the secretion of the anterior pituitary gland through the production and release of specific peptide hormones. Luteinising hormone-releasing hormone (LHRH) and thyrotrophin-releasing hormone (TRH) are two such peptides which have been fully characterised and synthesised^1,2. Studies on intact animals have revealed the importance of various neurotransmitters and hormones in the modulation of hypothalamic LHRH and TRH secretion but little is known of the cellular mechanisms involved in such control, especially at the neurosecretory nerve terminal. We have described^3,4 the use of nerve endings (synaptosomes) isolated from the mammalian hypothalamus to investigate factors which influence the release of corticotrophin-releasing factor (CRF). As this factor is uncharacterised, a major limitation of this work has been the use of bioassay techniques to measure indirectly corticotrophin-releasing activity. In the study described here radioimmunoassays have been used to measure the release of immunoreactive LHRH and TRH from synaptosomes prepared from rat and sheep hypothalami, and we report the influence of neurotransmitters and steroid hormones on these processes.